JXSC Mineral

Exploring Types and Features of Rotary Dryers

The rotary dryer has a wide application range, convenient operation, and a high operation rate. It is widely used in the cement industry to dry raw materials and fuels such as clay, slag, crushed stone, and coal. During drying, the hot air or hot flue gas transfers heat to the material to evaporate the water. At the same time, relying on the function of the ventilation equipment, the drying medium in the drying equipment is continuously updated to eliminate water vapor. There are also various forms of drying equipment. Commonly used in the cement industry are rotary dryers, fluid dryers, stirring (suspension) drying, active airflow drying pipes, etc. In recent years, spray drying devices are still being studied at home and abroad. These devices generally use hot flue gas for convection drying. The cylinder of the rotary dryer is generally a single straight cylinder. When installed, the cylinder is at an inclined angle to the horizontal. The material enters from the high end and slowly flows to the bottom with the rotation of the cylinder end and remove. In small and medium-sized cement plants, the cylinder length of the dryer is generally 6-20m to ensure the residence time of the material in the dryer and meet the drying process requirements. The hot air flowing out of the hot blast stove and the material exchange heat in co-current or counter-current in the cylinder.

Rotary Dryers Types

  • According to its heat transfer mode, the rotary dryer is divided into three types: direct heat transfer type, indirect heat transfer type, and multiple heat transfer type.

1. Direct heat transfer type

The high-temperature hot gas directly contacts the material in the cylinder and transfers heat to the material.
This type is suitable for drying materials that are not sensitive to high-temperature hot air and materials that are not afraid of coal ash pollution. The coal slime dryer belongs to this type of drying equipment.

2. Indirect heat transfer type

High-temperature hot gas heats the metal sleeve to transfer heat indirectly to the material. It is suitable for drying powdery materials that cannot be polluted by coal ash or are easy to raise dust. This type of heat transfer efficiency is poor.

3. Duplex heat transfer type

The high-temperature hot air first passes through the sleeve, and then indirectly transmits the hot air to the material through the sleeve, and then directly contacts and transfers heat with the material from the inside of the sleeve to the outside of the sleeve. It is suitable for drying materials that are easy to catch fire and explode, such as bituminous coal. The three-cylinder dryer belongs to this type of dryer.

Rotary Dryer
  • According to the running direction of the material and the high-temperature hot air, it is divided into two types: downstream type and countercurrent type.

1. Downstream type

In this type of dryer, the flow direction of the material and the high-temperature hot air flow is consistent.
The hot flue gas enters the dryer from the feed end and immediately contacts the wet material, and a large amount of material moisture is evaporated at the feed end.
Therefore, it is easy to cause uneven drying speed of materials in this dryer.
It suits materials with high initial moisture, low-temperature resistance, and low moisture absorption.

2. Countercurrent type

In this type of dryer, the material flows in the opposite direction to the high-temperature hot air flow.
The drying speed of the material in the dryer is relatively uniform because the average temperature difference between the reverse hot airflow and the material is larger, so its heat transfer efficiency is higher than that of the forward flow type.
Sludge dryers generally belong to this type.

Main Feature

  1. The rotary dryer has high thermal efficiency and an obvious energy-saving effect. After the dryer equipment is put into production, the coal-saving effect is obvious.
  2. The drying mechanism is scientific, reasonable, highly efficient, and energy-saving. The material exchanges heat with the hot air in the inner cylinder in the form of radiation, convection, and conduction, and in the outer cylinder in the form of conduction and convection.
  3. The length of the machine is shortened, which is beneficial to the process layout.
  4. The machine adopts the co-current drying process of materials and hot air flow and has a wide range of applications. It is suitable for drying various raw materials such as clay, coal, slag, iron powder, etc. It is also suitable for drying various bulk materials in metallurgy, chemical industries, and other departments.
  5. The machine is compact in structure. The whole machine is arranged horizontally, supported by supporting wheels, canceling the large and small gear transmission and replacing it with supporting wheel transmission, which makes the equipment installation more convenient, operation simpler, more reliable, and higher in operation rate.
  6. An automatic temperature monitoring system makes the operation more convenient.
  7. Various lifting plate designs, the organic combination of the angular lifting plate and the swivel lifting plate makes the material and hot flue gas exchange more fully and reduces the mechanism of the “wind tunnel” in the dryer cylinder.
  8. Adopt frequency conversion speed regulation, adjust the drum speed of the dryer equipment, and adopt an appropriate speed according to the incoming moisture and output requirements to ensure the needs of the next process.
  9. The outer surface area of this machine is more than 30% less than that of the single-cylinder rotary dryer, and the outer cylinder has a thermal insulation effect on the inner cylinder, the surface temperature of the outer cylinder is low, and the heat loss is small. At the same time, the working environment and working conditions have been greatly improved.

The rotary dryer is a versatile and efficient machine that can be used in many industrial drying processes. Its high productivity and ease of operation make it an ideal choice for many applications. It is especially useful in drying materials such as slag, clay, and coal powder which have distinct properties that require special care when drying. Its ability to rotate materials continuously has also been a major factor in its popularity over other dryers. With proper maintenance and use, this type of dryer can last several years without any major issues.